Pages

Friday, February 26, 2010

I listened in to parts of the Decadal Survey's steering committee earlier this week. A full morning was dedicated to the proposed Mars Sample Return (MSR) mission. (Presentations haven't been posted yet.) In its current form, the mission would consist first of the delivery of a rover that would collect and cache carefully selected samples. Four to six years later, an orbiter would be launched that would eventually receive samples from the surface and then return them to Earth. Two years after that, a lander would deliver a small rover that would fetch the cached samples and an ascent vehicle that would blast off from the surface and deliver the samples to the waiting orbiter. Total cost for the series of missions is current estimated to fall between $6-7B. (See Bruce Moomaw's descriptions of the current plan part one and part two or read a recent presentation at http://www.spacepolicyonline.com/pages/images/stories/PSDS%20Mars2%20Li-MSR.pdf.)

The most interesting part came in the discussion by the committee members after the final presentation. The point was made that at this cost, MSR would be NASA's mission of the decade and therefore could not fail. Another member described the proposed plan as too fragile because everything must work for the samples to finally return to Earth.

These comments got me to thinking. The MSR proposal involves three launches from Earth, four interplanetary cruises, three atmospheric entry and landings (on Mars) or recovery (on Earth), two rovers operating on Mars, a launch from the surface of Mars, and the transfer of the sample in Mars orbit from the Mars ascent vehicle to the waiting orbiter. I did a simple spreadsheet that looked at the effect of cumulative probabilities. The challenge is to know what probability of success to assign to each individual element. Since I don't know, I did a sensitivity analysis that first assumed 99% probability of success for each stage of the missions, resulting in a respectable 87% probability that all would succeed. But reduce the probability of success for each stage to 97%, and the overall probability drops to 65%. The odds of overall success drop to less than half if the probability of each element completing successfully drops to 95%. I also tried a version that assigned different probabilities to different mission stages based on a weak sense of how risky each one might be.

Editorial Thoughts: Unfortunately, assigning probabilities of success to mission elements is tricky. The goal is to have overall mission success in the high 90 percents. Those probabilities are modeled, not calculated from statistics. Except for launches (of which there are many) these are one of a kind experiments. (According to Wikipedia, the Delta II family had a 95% launch success rate over 300 launches.) What if Spirit's early memory problems had proved fatal? What if the fetch rover finds a sand trap it cannot get out of? What if winds cause a crash landing? A Mars sample return mission has at least two never tried before stages: launch off the Martian surface into an orbit matching the waiting orbiter and then successful rendezvous and transfer of the samples. Not all elements of these complex missions can be fully tested on Earth. There will be, for example, no full end-to-end testing of the Mars Science Laboratory's entry, landing, and descent until the craft reaches Mars.

Balancing this is the careful attention the mission designers put into trying to minimize the chance of failure partially by over designing and testing the systems and partially be operating them conservatively.

The most obvious solution to the problem of cumulative risk for MSR would be to duplicate each element. That strategy, however, probability would raise the overall program cost to over $10B and perhaps even to $12B.

An alternative strategy would be an adaptive approach. Hold off on building the orbiter and Mars ascent/fetch rover elements until you know that the caching rover has succeeded. Also have the caching rover leave duplicate caches. If the caching rover fails, build and fly a second copy.

Once you know that the samples are waiting to be picked up, fly the orbiter with enough resources to last in Martian orbit for many years. When building the Mars ascent/fetch rover, buy duplicates of key parts. Then if the first attempt fails (and possibly loses one of the cached sets of samples), figure out what went wrong and then build a second version.

Designing missions is not my area of expertise. JPL's engineers know probability statistics far better than I do, and so I'm sure they are looking for ways to address the problem of cumulative probability of success. They probably have a more clever approach in mind than what I've suggested. So think of this blog entry as raising a key problem that we haven't heard the solution to yet.

Wednesday, February 24, 2010

The last blog entry discussed the proposed NASA budget for FY11 and projected budgets through FY15. The overall NASA budget also calls for an extensive series of robotic "precursor" missions to the moon, Mars, and near Earth asteroids. The goals of these missions will not be scientific but rather will be to fly ahead of presumed eventual human missions to demonstrate technologies, assess potential resources to use, and determine if hazards are present.

The Lunar Reconnaissance Orbiter (LRO) and Lunar Crater Observation and Sensing Satellite (LCROSS) missions were flown under a similar program aimed at returning humans to the moon. What's new in this budget proposal is that the list of targets has been expanded to include Mars and the near Earth asteroids.

While these aren't science missions, it's likely that the missions will make measurements that are scientifically useful. LRO will be turned over to the planetary science program in the next few months to become a scientific mission once the primary mission of mapping the moon for future manned missions is completed. Looking ahead, exploring the craters at the lunar poles for ice also would provide valuable scientific data. It's hard to imagine that a mission could explore potential resources at a near Earth asteroid without making composition measurements that also would be scientifically valuable. And all these missions probably would carry cameras, so armchair explorers will get to see new sites in the solar system.

The proposed budgets for these missions is projected to grow considerably to be almost twice as large as the largest planetary science budget item (Mars) and be equal to more than half the entire planetary budget.

An additional key contributor to a robust exploration program will be the acquisition of critical knowledge gained through the pursuit of exploration precursor robotic missions. These missions will provide vital information—from soil chemistry to radiation dose levels to landing site scouting to resource identification—necessary to plan, design and operate future human missions. These missions will help us determine the next step for crews beyond low Earth orbit, answering such questions as: Is a particular asteroid a viable target for crewed mission? Do the resources at the lunar poles have the potential for crew utilization? Is Mars dust toxic?

NASA will send precursor robotic missions to candidate destinations for human exploration such as the Moon, Mars and its moons, Lagrange points, and nearby asteroids to scout targets for future human activities, and identify hazards and resources that will determine the future course of expanding human civilization into space. Projects will make critical observations, test approaches and operations concepts, and identify specific target destinations directly beneficial to future human space activities. Instruments, destinations and missions will be prioritized based on their utility to future human activities... While there may be some synergies between this program and the Planetary Science theme within SMD, care will be taken to avoid unnecessary duplication. Dedicated precursor exploration missions are planned to remain below $800 million in total cost, and most will be considerably less expensive.

NASA will begin funding at least two dedicated precursor missions in 2011. One will likely be a lunar mission to demonstrate tele-operation capability from Earth and potentially from the International Space Station, including the ability to transmit near-live video to Earth. This will also result in investigations for validating the availability of resources for extraction. NASA will provide opportunities to participate in the payloads and observation teams, and potentially portions of the spacecraft, through open competition.

NASA will also select at least one additional robotic precursor mission to initiate in 2011, and identify potential future missions to begin in 2012 and/or 2013. Potential missions may include:

Landing on asteroids or the moons of Mars rather than orbiting these bodies would allow us to better determine whether they pose safety hazards to astronauts or contain materials useful for future explorers. Landing can also test technologies that could help future human missions.

Landing a facility to test processing technologies for transforming lunar or asteroid materials for fuel could eventually allow astronauts to partially “live off the land.”

In Situ Resource Utilization: NASA will fund research in a variety of ISRU activities aimed at using lunar, asteroidal, and Martian materials to produce oxygen and extract water from ice reservoirs.

Autonomous Precision Landing: In FY 2011, NASA will initiate development of a flight experiment to demonstrate an autonomous precision landing and hazard avoidance system. NASA will pursue use of this system on the first robotic precursor exploration mission to the Moon or other planetary body.

Advanced In-Space Propulsion: NASA will work with partners in industry as appropriate, to conduct foundational research to study the requirements and potential designs for advanced high-energy in-space propulsion systems to support deep-space human exploration, and to reduce travel time between Earth’s orbit and future destinations for human activity. These technologies could include nuclear thermal propulsion, solar and nuclear electric propulsion, plasma propulsion, and other high-energy and/or high-efficiency propulsion concepts.

Entry, Descent, and Landing (EDL) Technology: NASA will develop and test concepts for large aeroshells and advanced thermal protection system materials to enable aero-capture and atmospheric entry of heavy payloads. These technologies will enable the demonstration of EDL capabilities on future robotic precursor and flagship missions.

Monday, February 22, 2010

NASA today released its detailed proposed budget for Fiscal Year 2011 (which starts this October). Normally this is released with the entire federal budget, but the big picture pieces of NASA's budget (read, manned spaceflight program) were not settled until a day or two before the release of the entire federal budget proposal. The budget package includes hard figures for the proposed FY11 budget and progressively softer projected figures for out years until 2015.

All figures are mine and are derived from the budget numbers in NASA's documentation.

As I previously reported based on a summary budget, NASA's planetary program is proposed to have a large (10.8%) increase from FY10 to FY11. Projected budgets show increasingly smaller annual increases that could well fall below the rate of inflation and could lose purchasing power over time.

Big winners in this proposal for FY11 are the Lunar program (31.9% increase), the Mars program (28%), and the technology program (19.7%). The planetary program does not have to include payment to restart the production of plutonium-238 within its budget. (I haven't looked elsewhere within NASA and DOE's budgets to see where the dollars are budgeted).

The budget apparently includes enough money in the Outer Planets program to fund early development of the Jupiter Europa Orbiter mission for the next year or two. However, to fly this mission around 2020, the outer planets budget has to increase by several hundred million a year by FY14. The budget documents state, "In FY 2010 and FY 2011 NASA will continue to provide funding for further definition study and technology development efforts for the Outer Planets Future mission while awaiting the results of the Decadal Survey establishing the science community's highest joint priorities. NASA will also continue to negotiate the details of potential partnerships with the European Space Agency (ESA) and other international partners." The budget line for Outer Planets also includes funding for the Casinni mission. Funding for the Cassini mission will be about $60M per year.

The Discovery and New Frontiers missions essentially continue unchanged with each showing small changes year-to-year as missions complete and ramp up development.

Editorial Thoughts: The one time budget increase is nice, but much of it's benefit could be lost due to future inflationary pressure. Given the increasing pressure to freeze or cut large portions of the federal budget, it's nice that if this budget is substantially approved by Congress that the figure to cut from in the future would start from a larger FY11 number.

There is a large mismatch between NASA's stated intention to fly JEO and the money projected in this budget. Put simply, if JEO flies, then something else must shrink or go away. Consider what would be needed if by 2015, JEO might need as much as ~$600M. To give you an idea of how challenging this would be, funding JEO at $600M in FY15 could be done by budgeting $100M from the Outer Planets program, eliminating the Lunar Quest program, eliminating the New Frontiers program, and taking about $150M from the Mars program (which would probably make Mars Sample Return undoable in the early 2020s.) I want to emphasize that I don't know the exact funding required by JEO in FY15; this is a guesstimate from figures published in EJSM Final Report. However, the actual figure will be large, and $500-600M is probably in the right ballpark.

Another alternative would be to plan a less ambitious outer planets program that focuses on several New Frontiers class missions instead of a single flagship mission. Over time, the total figure might be the same, but funding peaks could be lower. Here is what one program might look like (using projected FY15 budget numbers):

Mars $485M

Outer Planets $450M (more slowly implemented JEO or a series of New Frontiers class missions)

Discovery (for inner planets/primitive bodies) $313M

What would be lost under this concept would be the Lunar and New Frontiers programs.

It appears that NASA will make the final decisions on how to program future budgets based on the recommendations of the Decadal Survey. So I view the budget numbers past FY13 a simply running out the program as it is understood today. Depending on what the Decadal Survey proposes, budgets for FY14 onwards may look very different than what is presented here.

Additional Budget Background: The following paragraphs are quoted from the budget document and discuss what future programs would be funded.

Mars: "The Mars Reconnaissance Orbiter (MRO) and (if technically possible) both Spirit and Opportunity rovers (MER) will continue to explore and perform data analysis throughout FY 2011. Concept studies with the ESA-NASA 2016/2018 partnership missions will finalize and the Mars 16 mission will enter into formulation phase by the end of FY 2011."

Outer Planets: "NASA Cassini will continue its historic operations and data analysis. In FY 2010 and FY 2011 NASA will continue to provide funding for further definition study and technology development efforts for the Outer Planets Future mission while awaiting the results of the Decadal Survey establishing the science community's highest joint priorities. NASA will also continue to negotiate the details of potential partnerships with the European Space Agency (ESA) and other international partners."

Lunar: "LADEE completed its preliminary design review in FY 2009 and will enter Implementation Phase (KDP-C) in late FY 2010. The ILN/Lunar Surface Science mission will continue with its the risk reduction efforts during FY 2011. NASA will negotiate and work the Plutonium restart capability with DOE throughout FY 2011."

Discovery: "A new Discovery 12 AO selection will be made by the end of FY 2011 following the AO release in early CY 2010."

New Frontiers: "Having recently chosen three concept studies to pursue in 2010, NASA expects to select one New Frontiers 3 mission to proceed into Phase B (or an extended Phase A) by third quarter to late FY 2011."

Technology Development: "The In-Space Propulsion Program (ISP) will continue toward a completion of the NASA's Evolutionary Xenon Thruster (NEXT) electric propulsion life validation. The Radioisotope Power Systems (RPS) Program, working with the Department of Energy, will start the flight development of the Advanced Stirling Radioisotope Generator (ARSG) that would support a flight in the 2014-2015 timeframe. Furthermore, the RPS Program continues to develop technologies and processes to support current and future NASA missions. The Advanced Multi-Mission Operation System (AMMOS) project will continue to develop the multi-mission software tools for spacecraft navigation and mission planning throughout FY 2011."

Thursday, February 18, 2010

NASA's Stardust spacecraft just performed a trajectory correction maneuver to fine tune the timing of its encounter with the comet Tempel 1. Stardust, you'll recall, returned dust samples from the comet Wild 2 and now is in an extended mission to encounter Tempel 1. That latter comet was impacted by a projectile from the Deep Impact spacecraft. The primary goal of the Stardust encounter will be to image the crater produced by the Deep Impact projectile. The depth and form of that crater will tell us a lot about the surface properties of Temple 1. Imaging the crater was a key goal of the Deep Impact mission, but the crater could not be seen through the ejected cloud that resulted from the impact.

Meanwhile, the Deep Impact craft is on it way to its own second comet encounter with Hartley 2 on Nov. 4 of this year (http://epoxi.umd.edu/2science/objectives.shtml). Look about 2/3 of the way down this page for a nice explanation of the geology of Tempel 1, under the heading, Talps and Layers. Essentially, the surface of Tempel 1 is composed of layered piles (talps) that may have formed from low speed impacts. If you are interested in comets, this is an interesting read on the science that flyby missions can do.

Tuesday, February 16, 2010

Off and on for the last 25 years or so, aircraft have been proposed to explore Mars. Their advantage has been that they could study long swaths of the surface from elevations of just a few kilometers (compared to hundreds of kilometers for a low orbiter). Their disadvantage has been that Mars is hard to fly in -- the air at the surface is thin -- limited communications bandwidth, and power/fuel for only a few hours of flight. The last serious proposal for a Mars aerobot was the ARES proposal for a Scout mission competition. The mission wasn't selected, and the role of high resolution imaging has moved to orbiters with extremely powerful cameras (really small telescopes), long lifespans, and high data rates to Earth. (However, no platform has been flown to carry out an plane or balloon's role for in situ atmospheric studies or detailed subsurface mapping with ground penetrating radar.)

Now a proposal has been put forth for a Titan airplane as an alternative to the frequently discussed Titan balloon mission. Where Mars is hard to fly, Titan would be easy: Low gravity and a dense atmosphere make flight "over 1000 times easier at Titan than at Mars and more than 20 times easier than on Earth". (LPI abstract)" [I'm no fluid dynamicist, but flying in the dense atmosphere of Titan may be more akin to moving through water than flying as we know it in the comparatively thin fluid known as our atmosphere.] Essentially perpetual power could be provided by a plutonium-powered ASRG.

Up until this proposal, it has been presumed that in situ exploration within Titan's atmosphere would be conducted with a hot air balloon powered by the much heavier MMRTG plutonium power generators. While the MMRTG's contain more plutonium and produce more waste heat (useful for heating gases for a hot air balloon), the power-to-weight ratio of these generators was too low for use with an airplane. The much lighter ASRG units are a "game-changer" enabling powered flight by a propeller driven plane.

Either a balloon or an airplane platform would be a key element in exploring Titan. The hazy atmosphere of this moon makes it difficult to image the surface (although some near-infrared spectral windows exist). The depth of the atmosphere makes it impossible for an orbiter to hug this world the way that Mars orbiters can. At Titan, an orbiter would maintain a distance of 1500 km compared to the 300-400 km orbits at Mars. Within the atmosphere, high resolution images and radar soundings of the subsurface can be obtained. An in situ probe can also make detailed atmospheric composition and weather measurements impossible from an orbiter.

An airplane would have a number of advantages over a balloon:

The plane can remain constantly on the sunlit side of the moon and thus in direct communication with the Earth. (At the equator, the plane would have to average just 13-14 km per hour to remain on the sunlit hemisphere.)

While a balloon's flight would be at the whim of the winds, a plane could be directed to specific regions for study.

The plane's design and software could make use of the extensive heritage of design for unmanned aereial vehicles (UAVs) used by the military on Earth. For a platform that will have to operate autonomously for much of the time because of the time delay for commands from Earth, this is a key heritage.

The plane that has been proposed would be small, around 120 kg, about the same weight as the gondola of the proposed Titan Saturn System Mission Montgolfere. The published summaries of the plane proposal do not include a list of instruments and talk only about acquiring images. However, the TSSM planning documents provide a list of potential instruments for the balloon mission that would also be valuable on an airplane (TSSM In Situ Elements pages 53-54):

Visible imaging system (2 kg) with three wide angle and one narrow angle camera

In general, planetary probes can carry instruments weighing between 10-20% of their weight. Given this limitation, the plane could carry half to the full list compliment of this instrument list. However, space limitations might further limit the instrument compliment.

The proposers are pitching the mission as a stand alone Discovery or New Frontiers mission that would fly without a supporting Saturn orbiter for communications relay. They point out that the scientific results would be limited by the bandwidth of the antenna carried within the plane's nose. They propose that the plane would download thumbnail of the data gathered, with scientists on Earth deciding which subsets of full full data sets would be returned.

The authors of the abstract describing the Titan airplane provide a compelling case for the mission. The plane "allows directed exploration of Titan’s sand dunes, mountains, craters, channels, and lakes, features of primary geologic interest as evidenced by the number of journal articles on the topics over the past several years. Subsequent imaging can search for changes. The airplane can fly predesigned routes in order to build up large context mosaics of areas of interest, and then swoop down to low altitude to acquire high-resolution images at 30-cm spatial sampling similar to that of HiRISE at Mars. The elevation flexibility of the airplane allows us to acquire atmospheric profiles as a function of altitude at any desired location." (LPI abstract)

Editorial Thoughts: This is a bold and exciting proposal. It could significantly enhance our understanding of Titan by providing high resolution studies of the surface and atmosphere gathered over months to years. The ability to send the plane to specific regions of Titan to fly over the Xanadu highlands, cross the boundary from land to sea, or explore the river channels is absolutely compelling. The ARES proposal included a video camera (along with more scientifically oriented imagers) that would have allowed armchair explorers on Earth to ride along.

Because the mission builds upon the heritage of UAVs and Mars plane designs, the technology to implement the mission may be mature. Whether the technology is mature enough for flight is out of my expertise -- who but aerospace engineers could have judged that the proposed designs for Titan Montgolfere were too immature to fly? There is also the issue of plutonium supply for this mission. Right now, NASA would have enough for one Discovery mission and the Jupiter Europa Orbiter if Russia honors its contracts, which it currently is saying that it won't.

I am coming to personally favor a set of missions to the Saturn in the upcoming decade. A Titan atmospheric probe/lake lander would explore the chemistry of both fluid systems. A New Frontiers-class Titan-Enceladus Saturn orbiter would provide further studies with optimized instruments from a number of flybys of both moons. And either a balloon or plane (depending on technology maturity) would explore Titan from within the atmosphere. Preferably, the last mission would fly in conjunction with or after the Saturn orbiter so that the latter could provide a communications relay.

Unfortunately, the solar system is full of compelling targets. The series of modest Saturn system missions outlined above would total $3-4B if the lander and plane can fit within Discovery budgets and the orbiter within a New Frontiers budget. Add $3.2B for a Jupiter-Europa orbiter and $3-4B for Mars exploration, and you've spent most of NASA's projected budget of ~$13B for the coming decade and done nothing for exploring Venus, the moon, asteroids, or comets.. The Decadal Survey will have tough choices between excellent missions.

Friday, February 12, 2010

I'm finding that the subject of Enceladus missions intriguing, and thought I'd follow up on Wednesday's brief blog on possible Enceladus missions with a fuller description of a possible sample return mission.

I'll start with a report on the limitations of the Cassini mission to explore Enceladus (copied from the presentation, 2007 Enceladus Flagship Study):

The proposed LIFE (Life Investigation For Enceladus) mission addresses some of these limitations by flying a Stardust like mission to Enceladus. Stardust, you'll recall, flew through the the coma of a comet to capture samples of dust that were successfully returned to Earth. The LIFE mission would adopt a similar mission architecture and mission design philosophy. The latter focused on designing a mission that fit within the $164M cost commitment (not including launch vehicle). The Stardust project remained within that cost cap by refusing to accept mission creep. Worthwhile science investigations were not added if they did not contribute to the core requirement of collecting and returning samples to Earth. The proposal team does not give a cost for LIFE, but state that they believe it can come in under the previous $1.3-1.8B estimates for a sample return mission.

The LIFE mission would enter orbit around Saturn after an approximately eight years flight from Earth. The team proposes to encounter Titan one to two times for sampling of its upper atmosphere. (It's not clear if the sampling would be with in situ instruments or by the collection of material to return to Earth.) LIFE then would encounter Enceladus' plumes and the E-ring that contains material ejected from the plumes several times at speeds of 3-4.5 km/second (compared to Stardust's 6 km/s). After collecting the samples, the spacecraft would depart from Saturn on a five year return trajectory to Earth for a total mission duration of 13.5 years.

Samples would be collected by an aerogel collector modified to soften the impact for solid particles plus a 'volatiles trapping and sealing deposition' to collect samples of the gases. (Aerogel is one of the least dense materials known. Think of it as super styrofoam that can soften the impact of particles so that they remain intact for analysis on Earth. The LIFE mission would use a version of aerogel modified to better capture fragile material than was used for Stardust. I'm not sure what technologies would be used to trap the volatiles. A volatile collection device was proposed for Stardust but later dropped for reasons that I don't know -- perhaps cost.)

To preserve the integrity of the volatile samples, the collection system would be kept below -123 degrees Celsius. However, the presentation points out that even samples maintained at room temperature would still include important dissolved salts, dissolved organics, and insoluble particulates.

To contain costs, the instrument payload would be kept to a minimum. In addition to the sample collection devices, a mass spectrometer would measure the composition of the gases released from Enceladus and a magnetometer would help measure the internal structure of Enceladus by looking for induced changes in the magnetic field of Saturn. (It's not clear what the magnetometer would add over what Cassini's magnetometer can already measure.) Apparently cameras and a dust counter would be considered, but only if they fit within the cost target. (The presentation is not clear on this.)

Editorial Thoughts: I like the core of this mission concept. However, given the long flight times to reach Saturn, I don't think that flying the minimal mission makes sense. (The tightly focused Startdust mission made sense -- comet flyby mission opportunities are abundant and fairly inexpensive.) Even if LIFE were constrained to New Frontiers mission costs, the total mission would be over $1B once launch costs and other overhead were included. I think that the mission needs at a minimum to also carry an ice penetrating radar to directly measure the extent and depth of the ocean believed to lie within Enceladus and be the source of its plumes. I also think that a minimal remote sensing instrument suite consisting of a visible and thermal imager should be carried. The former can study the surface structure and pinpoint plume sources while the latter can measure the 'hotspots' that are the connection between the suspected ocean and the surface. The remote sensing instruments could be mounted so that they can study the surface during each flyby while samples are collected.

International involvement could help lower the costs of the mission. One agency, for example, could provide the spacecraft bus while another could provide the sampling system and return capsule. Instruments could be paid for by several nations.

If the mission is implemented by several nations, there might be a simple way to enhance the mission. The mission could be implemented as a two spacecraft system. A primary spacecraft could deliver the entire system to Saturn and carry the instruments. A return spacecraft would house the sampling system and carry the return capsule. Once the samples were collected, the return spacecraft would depart for Earth while the primary spacecraft would remain at Saturn for additional studies of Enceladus and perhaps Titan. (The Russian Phobus GRUNT mission uses a staged spacecraft system similar to this.) Different space agencies could implement each piece of the mission.

Wednesday, February 10, 2010

The latest results from Cassini's flybys of Enceladus increase the likelihood that this small moon has a liquid oceans and the conditions for life. (See BBC story among many.) That in turn increases the priority of Enceladus as a target for exploration in the coming decade. At the moment, the Decadal Survey is studying possible architectures for missions ranging from returning samples from the plume, to multiple flybys, an orbiter, or a lander. Unfortunately, missions to the Saturn system tend to be expensive, and even a minimalistic multiple flyby mission will probably exceed $1B. More ambitious missions such as landers or sample returns may well cost much more and would suffer from technical immaturity. (Which is what kept the Saturn Titan System Mission from being selected as the Flagship mission for the coming decade over the Jupiter Europa System Mission.)

While we wait to see what priority the Decadal Survey gives to Enceladus here are links you may want to follow:

Enceladus Sample Return (a la Stardust, with samples gathered during flybys through the plumes. I really like this idea, but think the Decadal Survey may find that cryogenic cooling is required to preserve the ices and any hydrocarbons, which would raise the technical difficulty)

Friday, February 5, 2010

The detection of methane in the Martian atmosphere has made trace gas measurements at this world a priority. The discovery implies that Mars is currently active -- methane has a short lifetime in the Martian atmosphere and must be regularly refreshed. However, the discovery brought with it two mysteries. First, is the source of the methane geological or biological activity? Either would have major implications for our understanding of this planet and the latter would have major implications for our understanding of our place in the universe. The second mystery is what is removing the methane so quickly, much more quickly than known processes could account for? The issue of trace gases is not limited to methane. Current plans are to explore concentrations of CO2, CO, H2O, H2O2, NO2 N2O, O3, CH4, C2H2, C2H4, C2H6, H2CO, HCN, N2S, OCS, SO2, HCl, and CO .

NASA and ESA have committed to flying a highly capable Mars Trace Gas Orbiter (MTGO) to address these questions in 2016. To give an idea of how capable this mission will be, the two space agencies are planning on a 125 kg science payload, slightly more mass than the instruments on either the Mars Reconnaisance Orbiter and the Mars Express missions. With launch, the mission is likely to be in the $700 - 750 M range.

This configuration does not include a high resolution imager, which is now included in the straw man instrument definition.

However, the investigation of trace gases will begin in 2012 with the Mars Science Laboratory, Curiosity. This rover will carry a tunable laser spectrometer which will measure the atmospheric composition. In addition to measuring the concentration of gases in the atmosphere, it will be able to measure carbon istotope in the methane. On Earth, life preferentally uses the lighter carbon-12 isotope; a similar bias on Mars would hint at a biological origin for the methane.

The 2016 orbiter has three goals related to trace gases; in order of priority they are (from the Joint Instrument Definition Team report):

"Detection of a broad suite of atmospheric trace gases and of key isotopologues;

"Characterization of the spatial and temporal variability of key species, including methane and ideally representing each family of photochemically important trace gases (HOx, NOx, hydrocarbons, etc.) and their source molecules (e.g., H2O); and

"Localization, including deriving the time histories of key species (again including, but not limited to, methane) and their possible interactions, including interactions with atmospheric aerosols and as affected by atmospheric state (temperature and the distribution of major source gases; e.g., water)."

Achieving these goals will require measuring changes of gas concentrations as they change with time of day, season, and transport from their sources by winds. Localization of sources is expected to be difficult given the dynamic nature of the atmosphere and changing concentrations of gases.

While the payload is justified on the basis of studying trace gases, the instrument payload will also continue climatological studies that began with NASA missions in the 2000s and carry out high resolution (1 - 2 m) imaging of the surface. The high resolution camera expected to be carried by the orbiter is likely to be less capable than the MRO HiRISE instrument. The former has approximately 25 kg allocated while the latter weighed in at 63 kg. Improvements in electronics will help make up the difference, but as I understand the mass allocations, substantial portions go to the the mechanical structure. (These imagers are essentially small telescopes.) In order of priority, the high resolution cameras goals are resolution, color differentiation, and stereoscopic capabilities.

In addition to the science goals, the mission will deliver an ESA technology demonstration lander and provide data relay for the 2018 rover(s) and possibly later landed missions. The mission will be jointly implemented by the two space agencies. NASA will provide the launch vehicle (> $200M), the Electra relay package, a Ka-band (high data rate) string for the orbiter's communications subsystem, $100M for the science package, and science operations lead. ESA will provide the spacecraft and manage the mission. Individual European nations will also contribute towards the instrument costs. (For ESA missions, the instruments are paid for by the individual nations whereas NASA pays for the instruments in its missions.)

If MSL and MTGO substantiate the presence of trace gases tied to geological or biological activity, several types of follow up missions are possible:

A Mars Organics Observer could continuously image Mars from the Mars-Sun L1 Lagrange point, and would eventually pinpoint sources of trace gases to within a handful of kilometers. This would be a Discovery class mission.

Balloons could monitor trace gases from within the atmosphere at different altitudes and locations

Aircraft could study trace gas concentrations within a local area

And if sources of trace gases can be localized to within a few kilometers, rovers or static landers with deep drilling capabilities could explore these sources in detail.

Thursday, February 4, 2010

In an expected move, NASA approved the extension of the Cassini mission for another ten years into 2017. Called the Solstice Mission (previously referred to as the XXM mission), this extension would be an exciting new mission in its own right:

Over 50 flybys of Titan, 11 of Enceladus, and 12 of other moons

Continued observations of Saturn and its rings as the season changes from equinox to solstice

Twenty orbits with the periapses just outside the F ring for detailed measurements of the rings mass and structure

Twenty-two orbits with the periapses inside the rings and just above the atmosphere for studies of Saturn's interior (to be followed by Cassini's plunge into the atmosphere at the end of the mission)

Monday, February 1, 2010

If you are interested in policy and the budgets that support them, this post provides links to a number of other sites. The big news in this budget proposal is on the manned exploration side, and some of the links below discuss these implications.

Before I list the links, here are a couple of more thoughts:

The increase in the Planetary program may be to pay for the production of plutonium-238. Last year, Congress complained that the Department of Energy (which by U.S. law is the only agency allowed to produce these nuclear materials) was bearing the budget hit for new Pu-238 production. The increase to next year's budget may be to move that hit to NASA (who would just funnel the funds to DOE).

In an e-mail discussion, Phil H. points out that the new Precursor program might fund the Lunar sample return that is currently a candidate for the next New Frontiers slot. I think this is possible (and almost any speculation is possible right now given the scarcity of details on this new program). However, the near Earth asteroid mission that is currently in competition would be an equally good candidate for this program. Given that all three contenders would make excellent choices (the third is a Venus lander), I'd love to see one or more of them flown under a separate budget.

Summary documents for the President's proposed fiscal year 2011 (which starts this coming October) have been posted. (For international readers, the budget will be modified by both houses of Congress, then the differences reconciled, and then the President will sign the final bill after possible negotiations with Congress.)

There are two good pieces of news. First, the budget proposes a 10.8% budget increase for 2011 over the 2010 budget. The the budget proposes to approximately match the inflation rate (presuming a 3% inflation rate). If this were to continue over a decade, NASA's purchasing power would increase by approximately $1B, or almost enough to pay for a New Frontiers mission. In a year where flat budgets are proposed for most discretionary spending, this is a substantial increase. Depending on the priorities set in the Decadal Survey, this budget increase may have been included to begin serious funding of the Jupiter Euorpa Orbiter.

All figures in $Ms.

The second piece of good news is that the budget proposes a series of robotic precursor missions to various solar system locations. Details on this new program are sketchy at the moment. Science appears to be a low priority, but for many locations, even a simple camera can lead to new understanding. It appears that the funding for these missions will come from NASA's Exploration budget, and therefore are in addition to the Planetary budget.

The proposed budget favors Earth Science and the Planetary program among NASA's science program:

Before celebrating, we should see how this proposal fares in Congress. In a year when a lot of popular programs will be held to flat budgets, raiding programs that are targeted for increases may be popular.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.